Supporting emergency calls on a wireless local area network

ABSTRACT

A device for identifying an emergency call in a wireless local area network includes an indicator to identify a call as an emergency call. The indicator can be a bit flag or an information element. The information element can include location information regarding the location of the station that placed the emergency call. This information can be used to located the caller. The location information can be transmitted from the station to an access point separately from an emergency call.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Nos.60/569,014, filed May 7, 2004, and 60/643,190, filed Jan. 11, 2005,which are incorporated by reference as if fully set forth herein.

FIELD OF INVENTION

The present invention generally relates to wireless local area networks(WLANs), and more particularly, to supporting emergency calls in a WLAN.

BACKGROUND

Existing 802 technology (802.11 WLANs, 802.15 wireless personal areanetworks (WPANs), etc.) traditionally does not have to support emergencycalls like cellular does. For cellular, support of emergency calls oftenresulted from regulatory requirements imposed on the technology and istherefore widely implemented in most of today's deployed wirelesscellular networks and handsets. Support for emergency calls involvesmany aspects across all communication layers, especially signalingsupport and mandated procedures, which are non-existent for 802.11 and802.15 technologies. With the advent of voice over Internet Protocol(VoIP) in WLANs and increased everyday usage of WLANs, support foremergency calls in WLANs will become necessary.

Even “fixed” VoIP phone service offerings for the residential markethave limited emergency call support. Number location information cannotalways be tracked by a dispatcher in a public safety answering point(PSAP), call back is not always possible, and address registration maybe required upon purchase of the equipment. When the VoIP phone is movedto a new location, the emergency call will still be sent based on theregistered address location. The registered address can be changed inprinciple, but delays are at least on the order of days or weeks inupdating the information at the PSAP. In addition, some users might notupdate their registration information in a timely manner, if at all.

This situation worsens with more mobility as enabled by VoIP phonesusing WLANs. WLAN based VoIP phones can work from any location and theuser can be expected to roam seamlessly between locations, such as froman office to a home to public hotspots, etc.

Certain 802.11-specific issues exist, including radio access, accesspoint (AP) location, caller location, and emergency call admission. Inregard to radio access, no priorities for emergency calls currentlyexist in the 802.11 standards, and there is no means to distinguish anemergency call from a regular call for the WLAN access network. Thelocation of an AP or a STA is currently unknown to the network in anon-proprietary manner, even if for example, the AP's identification caneasily be determined. It is also not currently possible to map thecaller's location in a non-proprietary manner.

In regard to admission, a tightly managed WLAN may prevent emergencycallers from establishing an emergency call if the caller is notauthorized to enter the network. The normal connection procedure betweena STA and an AP requires the STA to send an Association request,followed by negotiation with the AP prior to associating the STA to theAP. If the STA is unable to indicate that it is making an emergencycall, it would have to go through the entire association procedure todetermine if it could be admitted. As an example of this type ofdifficulty, if a STA does not have the proper password or authenticationcredentials to access the system (if the AP is configured to requirepasswords or require authentication credentials, as might exist forexample with a private hotspot or enterprise/office WLAN), the AP willbluntly refuse the STA's association request. But even if the STA hasthe proper password or authentication credentials, the AP could stillrefuse admittance to the network based on its configured maximumcapacity for voice users. In this case, the right decision for the APwould be to admit this new emergency call (at the highest priority) andto discontinue another existing voice call. Because the AP currentlylacks means to make this distinction in the first place, such a featurecannot be implemented with existing state-of-the-art WLAN technology.Contrast this with the operation of a cellular system, in which anydevice can make an emergency call, even a device without a SIM card.

SUMMARY

The present invention proposes various system operation aspects forenabling emergency call handling support with 802.11 and 802.15technology. Some of the proposals pertain to new L2 signaling messagesor information elements to indicate emergency calls to APs. Newprocedures and control mechanisms are proposed for emergency situations.In addition, procedures for dual-mode (WLAN and second generation (2G)or third generation (3G) cellular) implementations are addressed.Because emergency call requirements are often coupled to regulatoryrequirements on location reporting of the emergency caller's position,means and signaling procedures are proposed to allow requesting andreporting of geographic positions in a WLAN network. The positioninformation can be coupled to emergency calls or can be implementedseparately.

A benefit of a STA being able to identify an emergency call is thatsimple logic can be installed at the AP that allows the AP todistinguish between a STA that it should treat normally (i.e., shouldfollow regular association procedures) and a STA that should be admittedunder all circumstances, regardless of how the network is configured(i.e., bypass any security requirements to admit an emergency call).

A device for identifying an emergency call in a wireless local areanetwork includes an indicator to identify a call as an emergency call.The indicator can be a bit flag or an information element.

A device for reporting location information of a station in a wirelesslocal area network includes a location information field.

A method for placing an emergency call by a STA on a WLAN begins by theSTA placing the emergency call. A determination is made whether the STAis capable of operating on a cellular network. The emergency call iscontinued on the cellular network if the STA is capable of operating onthe cellular network. Then, a determination is made whether theemergency call was completed on the cellular network. If the emergencycall was not completed on the cellular network, then the emergency callis continued on the WLAN.

A method for locating a user placing an emergency call from a STA on aWLAN begins with the user placing the emergency call on the STA.Emergency signal frames are transmitted from the STA for a predeterminedperiod of time, whereby the emergency signal frames can be received byan emergency worker to locate the user.

A method for locating a user placing an emergency call from a STA on aWLAN begins with the user placing the emergency call on the STA.Emergency signal frames are transmitted from the STA and are received byan emergency worker. A determination is made whether the emergencyworker is within a predetermined range of the user. When the emergencyworker is within the predetermined range, a direct connection betweenthe user and the emergency worker is established.

A method for supporting an emergency call in a WLAN begins by placing anemergency call by a STA on the WLAN. The emergency call is received byan AP on the WLAN. A determination is made whether the STA hassufficient capabilities to complete the emergency call. The AP acts as aproxy for the STA if the STA does not have sufficient capabilities tocomplete the emergency call.

A method for maintaining location information at an AP for a STA in aWLAN includes receiving location information from the STA at the AP andstoring the location information at the AP.

A method for maintaining location information at an AP for a STA in aWLAN begins with the AP polling the STA to receive location information.The location information is reported from the station to the AP and isstored at the AP.

A method for placing an emergency call on a WLAN begins by sending aready to send (RTS) frame from a STA making the emergency call to an AP,the RTS frame containing an indicator that the STA is making anemergency call. The RTS frame is received at the AP and non-emergencySTAs are backed off, whereby the STA making the emergency call canaccess the network prior to the non-emergency STAs.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred embodiment, given by way ofexample, and to be understood in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a diagram of a standard medium access control (MAC) frame;

FIG. 2A is a diagram of a MAC frame with a bit flag indicating anemergency call;

FIG. 2B is a diagram of a MAC frame with an information element (IE)indicating an emergency call;

FIG. 3 is a diagram of a standard ready to send (RTS) frame;

FIG. 4A is a diagram of a RTS frame with a bit flag indicating anemergency call;

FIG. 4B is a diagram of a RTS frame with an IE indicating an emergencycall;

FIG. 5 is a flowchart of a method for using a RTS frame as shown inFIGS. 4A or 4B;

FIG. 6 is a flowchart of a method for switching radio technologies tocomplete an emergency call;

FIG. 7 is a diagram of a SOS beacon frame indicating an emergency call;

FIG. 8 is a flowchart of a method for transmitting and using the SOSframe shown in FIG. 7; and

FIG. 9 is a flowchart of a method to determine whether to apply a proxyfunction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the term “station” (STA) includes, but is not limited to, awireless transmit/receive unit, a user equipment, a fixed or mobilesubscriber unit, a pager, or any other type of device capable ofoperating in a wireless environment. When referred to hereafter, theterm “access point” (AP) includes, but is not limited to, a basestation, a Node B, a site controller, or any other type of interfacingdevice in a wireless environment.

The present invention is applicable to all WLANs, personal area networks(PANs), and metropolitan area networks (MANs), but in particular to802.11-based WLANs, 802.15-based wireless PANs, 802.16/20 based wirelessMANs, and equivalents thereto. In one realization, the present inventionis applicable to WTRUs implementing a combination of these accesstechnologies including WLAN, PAN, MAN, and cellular multi-mode WTRUs.

The present invention for handling emergency support will be describedhereinafter as being grouped into three major areas. This is, however,for convenience of explanation and should not be taken as a limitationof the invention.

I. Air interface related signaling/support and procedures

A. Indication of emergency calls in MAC frames and MAC signalingmessages

A standard MAC frame 100 is shown in FIG. 1. The MAC frame 100 includesa frame control field 102, a duration/ID field 104, one or more addressfields 106 a-106 d, a sequence control field 108, a quality of service(QoS) control field 110, a frame body 112, and a frame check sequence(FCS) field 114. The QoS control field 110 is divided into a pluralityof subfields, as shown.

A priority for emergency calls can be indicated in MAC frames by a bitflag, by an emergency message type IE, by an emergency message fieldpart on an existing or new IE, or by an emergency call code implementedusing a reserved (currently unused) value in any existing IE or field ofa MAC frame. The indicator allows an AP to know that it needs to admitthe emergency call. For similar purposes, QoS priorities or requirementsare indicated by means of QoS classes (for example DiffServ). Anyexisting MAC frame type (control, management, or data) can be modifiedto include the emergency call indicator. The emergency call indicatorcan be added to any location in the MAC frame, in the header or the bodyusing any of the mechanisms described.

As shown in FIG. 2A, a MAC frame 200 includes fields 202-214, which arethe same as fields 102-114 described above in connection with FIG. 1. Inone embodiment, a simple bit flag 220 is used to indicate to thereceiver that this is an emergency call. As shown in FIG. 2A, onepossible location for the bit flag 220 is in the reserved bit (bit 7) ofthe QoS control field 210. A person of ordinary skill in the art wouldnote that it is possible to place the bit flag 220 in any currentlyreserved location in any of the existing header or frame body fields inthe MAC frame.

As shown in FIG. 2B, a MAC frame 250 includes a frame control field 252,a length field 254, and an emergency call IE 256 to indicate anemergency call. The emergency call IE 256 can include, but is notlimited to, an emergency call flag 260, a reason code field 262, acapability information field 264, a location information field 266, avoice codec application field 268, and additional fields 270. Theemergency call IE 256 can be added to any MAC frame. In addition, theinformation contained in the emergency call IE 256 can be added to anexisting IE type.

The emergency call flag 260 can be a simple indicator (e.g., a bit flag)to identify that the call is an emergency call. The reason code field262 indicates the reason for the emergency call (e.g., fire, medicalemergency, etc.). The capability information field 264 includes thecapabilities of the STA placing the emergency call and is used to assistin completing the emergency call as quickly as possible. The locationinformation field 266 contains the location of the STA placing theemergency call. The voice codec application field 268 identifies thevoice codec used by the STA, and is used in case there is anyincompatibility between the STA and the AP attempting to handle theemergency call. Additional information that can be included into theemergency call IE (as fields 270) are timestamps and WTRU and/oroperator service capability information.

Existing MAC frames under 802.11e have call priorities. The TransmissionSpecification (TSPEC) IE includes a three bit priority subfield in atransmission specification information field. The principles of thepresent invention can also be implemented in the TSPEC IE by defining avalue for an emergency call. In cellular systems, a similar mechanism (asignaling frame) is used to send the call parameters to the network andincludes a reserved field to identify emergency calls.

B. Location information

Location information can also be attached to these new MAC frames 200,250 (e.g., in the location information field 266), in addition toconveying the emergency call establishment reason. For example, the APor STA can use the basic service set (BSS) ID, the AP or STA MACaddresses, static or dynamically assigned IP addresses, or globalpositioning system (GPS) information from an AP or STA implementing thisfunctionality, and forward this information to the emergency callcenter. It is noted that the location information can also be conveyedseparately from the emergency call information.

Other means of locating the emergency STA include, but are not limitedto, identifying the STA placing the emergency call by caller ID,utilizing a callback number, and using known addresses to help locatethe STA by the emergency call center (e.g., using the MAC addresses ofthe current point of attachment for the STA, such as the AP or thenetwork ID, or AP geographical coordinates).

For example, a MAC signaling mechanism for a WLAN can be used where theAP can request the position from a STA. The STA would report back to theAP with its position. One possible implementation includes the use ofassisted GPS (A-GPS) coordinates, that are currently in widespread usein cellular handsets. Multiple positioning methods can be supported fordifferent access networks, including, but not limited to, uplink timedifference of arrival (U-TDOA), enhanced observed time difference(E-OTD), idle period downlink observed time difference of arrival(IPDL-OTDOA), A-GPS, Universal Geographic Coordinates (for example, asdefined in IEEE standard 802.11k or IETF RFC 3825) and methods usingWLAN AP locations, cell site, or sector information and timing advanceor roundtrip time measurements. While the preceding examples ofconveying location information have been particularly mentioned, oneskilled in the art would note that any format to convey geographiccoordinates can be used.

The emergency call functions can be performed independently from (yetcomplementary with) the location reporting functions. To illustrate, itis possible to: (1) attach location information to the emergency callsignaling frames when the STA actually issues the emergency call, and(2) signal location updates as a stand-alone functionality without anemergency call. An example of the latter would be to keep the APinformed and updated about the latest STA position either periodically(e.g., every few seconds), polled as part of the AP backgroundoperation, or by unsolicited regular location reporting by the STA tothe AP. Maintaining location information at the AP may be preferablebecause when the STA issues the emergency call, the AP already has areasonably recent estimate of the STA's position, such that the STA isnot required to explicitly piggyback its location onto the emergencycall request.

For example, such stand-alone STA location information reporting can beused to allow implementation of location-dependent services in a WLANnetwork, in parallel to addressing regulatory requirements.

As such, the position information can also be provided to locationservices (LCS) applications existing within an interworking WLAN(I-WLAN), public land mobile network (PLMN), or in the STA. In addition,the originating party's serving cell identity or serving AP identity canbe provided to the LCS client.

C. Extend the existing RTS/CTS frame exchange mechanism and procedure

A standard RTS frame 300 is shown in FIG. 3. The RTS frame 300 includesa frame control field 302, a duration field 304, a receiver address (RA)field 306, a transmitter address (TA) field 308, and a FCS field 310.

A STA that wants to transmit an emergency call transmits an extended RTSframe 400 containing a special signaling flag as shown in FIG. 4A or anextended RTS frame 450 containing a new IE as shown in FIG. 4B.

FIG. 4A shows an RTS frame 400. Fields 402-410 of the RTS frame 400 arethe same as fields 302-310 of the RTS frame 300 described above inconnection with FIG. 3. The frame control field 402 has severalsubfields, including a protocol version subfield 412, a type subfield414, a subtype subfield 416, a to distribution system (DS) subfield 418,a from DS subfield 420, a more fragments subfield 422, a retry subfield424, a power management subfield 426, a more data subfield 428, a WiredEquivalent Privacy (WEP) subfield 430, and an order subfield 432.

The signaling flag can be added to any reserved bit in the RTS frame400. Potential locations for the reserved bit include the protocolversion subfield 412, the type subfield 414, and the subtype field 416.It is noted that one skilled in the art could place the signaling flagin any reserved bit in the RTS frame 400.

FIG. 4B shows an extended RTS frame 450, including a frame control field452, a duration field 454, a RA field 456, a TA field 458, a purpose IE460, and a FCS field 462. The purpose IE 460 can be similar in contentto the emergency call IE 256, described above. All STAs receiving theextended RTS frame 450 are then required to stop any transmissionattempt for a pre-determined amount of time to idle the wireless mediumand to give the STA in emergency an opportunity to transmit.

In one embodiment, upon receipt of an extended RTS frame, the receivingSTAs enter a modified backoff process in order to give the STA placingthe emergency call a higher probability to succeed in obtaining accessto the medium. Two implementations of modifying the backoff process arepossible: (1) shortening the backoff time for the STA placing theemergency call relative to other STAs, or (2) lengthening the backofftime for non-emergency STAs. In either implementation, the end result isthat the emergency STA has a shorter backoff time than non-emergencySTAs.

A method 500 for using the RTS frame 400 or 450 is shown in FIG. 5. Thepurpose of the method 500 is to idle the transmission medium in order topermit a STA to transmit an emergency call. The method begins with a STAplacing an emergency call by sending a RTS frame 400 or 450 (step 502).An AP receives the RTS frame (step 504) and responds to the STA with astandard CTS frame (step 506). The backoff type to be used by the AP isdetermined (step 508). There are two possible backoff types, both ofwhich would permit the STA placing the emergency call to access themedium prior to all other STAs waiting to transmit.

If the backoff type is that the STA in emergency (i.e., the STA placingthe emergency call) has a shorter backoff time, then the STA inemergency waits for the shortened backoff time (step 510) and thentransmits the emergency call (step 512). All other STAs that areattempting to access the medium wait for the standard backoff time (step514) and are then able to transmit (step 516). The method thenterminates (step 518).

If the backoff type is that all other STAs have a longer backoff time(step 508), then the STA in emergency waits for the standard backofftime (step 520) and transmits the emergency call (step 522). All of theother STAs wait for a longer backoff time (step 524) and are then ableto transmit (step 516). The method then terminates (step 518).

In general, when a STA enters a backoff procedure, the STA attempts totransmit randomly in one out of a series of N timeslots. If there is atransmission collision, the STA will backoff again and increase thevalue of N, up to a predetermined maximum value for N. Before a STA canattempt to transmit, the STA must wait for M timeslots. This basicprocedure provides any STA an equal chance of winning access to themedium. In 802.11e, to implement QoS, there are two ways to ensure thata particular station has a greater chance of winning access to themedium. The first is to reduce the value of M, thereby giving the STA ashorter wait time. The second is to use a smaller value for N, whichincreases the chances that a STA will be able to transmit in aparticular timeslot.

In the method 500, there are several possible means for a STA to knowwhich backoff value to use. A first means is to use hard-coded valuesfor M and N in connection with an emergency call, such that thesehard-coded values for M and N will be used by a STA in emergency. Asecond means is to explicitly signal values for M and N from the AP tothe STA in emergency. The AP would typically send those parameters tothe STA by either using broadcast or dedicated management frames duringnormal system operation. STAs read the emergency call-relatedconfiguration parameters to be used in case they need to set up anemergency call. One example is that the AP, as part of the Beacon orProbe Response management frames, sends other BSS configuration valuesto all STAs in its BSS. Adding the emergency call-related M and Nparameters is a natural extension to these. For example, 802.11eQoS-related configuration parameters per access category (backoffvalues, windows, etc.) to be used by all STAs in the BSS are signaledtoday by the AP using a similar mechanism.

A third means is a combination of the first and second means, by which aSTA has hard-coded default values for M and N that it uses normally, andif the STA is in emergency, the AP will signal new values for M and N tooverride the hard-coded default values. One skilled in the art couldenvision additional means for communicating the appropriate backofftimes to a STA in emergency and all other STAs seeking access to themedium.

D. Mandated switch-over to another radio technology for dual-mode WLANSTAs (for example 3G and WLAN)

In case of an emergency, a dual-mode WLAN STA will attempt any emergencycall first on the cellular network, instead of on the WLAN. This is inprinciple a “hard-coded” procedure in the STA alone. A method 600 forimplementing this procedure is shown in FIG. 6.

The method 600 begins by the user making an emergency call at the STA(step 602). A determination is made whether the STA is capable ofoperating on a cellular network or a WLAN (step 604). If the STA isoperating on a cellular network (i.e., is currently connected to thecellular network), then the STA remains on the cellular network for theemergency call (step 606). If the STA is capable of operating on thecellular network, but is not presently connected to the cellularnetwork, then the STA establishes a connection to the cellular network(step 608) and makes the emergency call on the cellular network (step606). If the STA is operating on a WLAN, then the STA switches to thecellular network to make the emergency call (step 610).

After the emergency call has been placed, a determination is madewhether the emergency call went through on the cellular network (step612). If so, then the method 600 terminates (step 614). If the emergencycall did not go through on the cellular network, then the STA switchesto the WLAN to make the call (step 616) and the method terminates (step614).

In case an emergency call needs to be issued by a dual-modeWLAN-cellular handset, the preferred procedure is to have the handsetfallback onto the cellular modem (i.e., establish the emergency call ona cellular radio link), because emergency call support may not beavailable or may be less reliable over the WLAN.

Alternatives for the method 600 include: (1) establishing a preferred,mandated, or recommended order of radio technologies (e.g., WLAN orcellular) to switch to when attempting to send an emergency call; (2)the system operator configures emergency call behavior on a SIM card orsimilar device for dual mode handsets; (3) maintain a VoIP call on thecellular network or move the call onto a traditional circuit switchedvoice channel in case of an emergency; (4) the system operator signals apreferred local order of radio technologies over the wireless interface;or (5) the user manually configures the policy setting.

E. Bypassing authentication and security when attempting an emergencycall

A procedure is mandated that any 802.xx STA seeking to establish anemergency call in a WLAN must be allowed by the AP. This includesbypassing authentication like 802.1x and other security measures on thenetwork side. This procedure could be triggered by using the extendedRTS/CTS method 500 (as shown in FIG. 5) or by a bit flag, IE, header,reserved information field, or bit/sequence value in the MAC frame (asshown in FIGS. 2A and 2B).

II. WTRU behavior/procedure in case of emergency

A. WLAN sends SOS beacon signal to facilitate in finding the caller

A procedure is mandated in the STA or configured by the network thatonce the emergency call is over (or even during), the STA and/or theinvolved AP start transmitting SOS type signaling frames 700 as shown inFIG. 7 on regular intervals.

An SOS signaling frame 700 is a modified version of a Probe Requestframe. The SOS signaling frame 700 includes a frame control field 702, aduration field 704, a destination address (DA) field 706, a sourceaddress (SA) field 708, a BSSID field 710, a sequence control field 712,a SSID IE 714, a supported rates IE 716, and an emergency call IE 718.The emergency call IE 718 can be the same as the emergency call IE 256described above in connection with FIG. 2B. It is noted that thesupported rates IE 716 is optional, and can be eliminated from the SOSsignaling frame 700 without affecting its functionality.

In one embodiment, the SOS signal frame can be defined as a ProbeRequest frame sent with short interframe space (SIFS) priority orpriority interframe space (PIFS) priority, to ensure access to themedium. The SOS signal frame contains new emergency call relatedelements in emergency call IE, such as 911 ID (e.g., caller ID),equipment details (such as international mobile equipment identification(IMEI)), network affiliations, user name, and emergency reason code. Thereason code may be obtained by the device prompting the user to identifythe reason for the emergency call (e.g., “press 1 if fire emergency”,etc.). A reason code would provide some ability to handle the emergencyin case there is no way to terminate the in-progress call.

The SOS signal frame can be scheduled for transmission every 100 mSec orso to facilitate location logging and tracking. An AP would be requiredto log any SOS signal frame reception with a timestamp and details ofthe signal. The signal strength details include signal strength, signalquality, antenna azimuth and gain, and caller details such as IMEI, username (if available), and other 802.11 device information useful foridentity and capability purposes. An AP receiving an SOS signal framewould also be required to report the event to an emergency network noderesponsible for emergency response, radio resource coordination,location, and tracking of the calling device.

This is an active probing mechanism where the SOS signaling frames aresent and can be received by emergency workers as they approach thecaller. One analogy is the emergency beacon in the black box of anairplane. A new MAC frame can be introduced for this purpose or anexisting MAC frame, for example a probe request frame, can be extendedby new IEs (such as the emergency call IE 256) to fulfill this purpose.

A method 800 for utilizing a SOS signaling frame is shown in FIG. 8. Theuser makes an emergency call from a STA (step 802). The STA begins totransmit SOS frames (step 804). Based on the desired implementation, theSOS frames can either be sent as probes or be used to establish a directconnection with an emergency worker (step 806).

If the SOS frames are to be sent as probes, a transmission period is setand a determination is made whether the end of the transmission periodhas been reached (step 810). If the transmission period has not ended,then the STA continues transmitting the SOS frames (step 812) and themethod returns to step 810. If the end of the transmission period hasbeen reached (step 810), then the STA stops transmitting the SOS frames(step 814) and the method terminates (step 816).

If the SOS frames are to be used to establish a direct connection withan emergency worker (step 806), then a determination is made whether theemergency worker in within range of the STA (step 820). If the emergencyworker is not within range of the STA, then the STA continuestransmitting SOS frames (step 822) and the method continues with step820. If the emergency worker is within range of the STA (step 820), thenthe STA stops transmitting SOS frames and establishes a directionconnection between the caller and the emergency worker (step 824) andthe method terminates (step 816).

In a first alternative (steps 810-814), the SOS frames transmitted bythe STA could be triggered by signaling from the AP or higher layerprotocols like session initiation protocol (SIP) once the emergency callis over. The duration/frequency of the SOS frames are contained in thistrigger signal. Sending the SOS frames after the emergency call is overprevents transmission of unnecessary SOS frames in case the emergencycall was a mistake or if there was no need for an emergency worker tocome in response to the call.

In a second alternative (steps 820-824), a direct VoIP connectionbetween the emergency worker and the caller is established when they arewithin range of each other. Other STAs that hear the SOS frames maytreat the SOS frames like the extended RTS frame described above inconnection with FIGS. 4A, 4B, and 5 (i.e., the other STAs will not tryto access the medium, so that the emergency caller has better access tothe bandwidth).

B. Network (for example, the AP) implements a call back functionality tohandle emergency calls

Once an emergency call is established, the WLAN maintains an activeconnection to the user that initiated the emergency call for a certainperiod after the emergency call is over in case of call back. Thisfunctionality may be transparent to the user.

III. Functionality in the infrastructure

A. Proxy function

A method 900 for determining whether an AP needs to act as a proxy forthe STA is shown in FIG. 9. The STA makes an emergency call (step 902)and the AP receives the emergency call (step 904). A determination ismade whether the STA has the capabilities to complete the emergency callbased on the network used to carry the call (step 906). The AP checks ifthe STA has all required functionality (e.g., SIP/H.323 protocoltermination, vocoder, etc.) to support the call. This information may beindicated as part of the MAC frame (e.g., MAC frames 200, 250) or it maybe part of the subscriber information in the network that the AP canaccess.

If the STA has all of the necessary capabilities, then the STA proceedswith the call as normal (step 908). The AP can add location informationto the call as necessary, including the location of the STA and/or thelocation of the AP (such as the network ID, the AP's MAC address, etc.)(step 910). The method then terminates (step 912).

If the STA does not have all of the necessary capabilities to completethe call (step 906), then the AP acts as a proxy for the STA, providingany necessary functionality (step 914). The AP adds location informationto the call as needed (step 910) and the method terminates (step 912).

If the AP determines that the STA does not have all the requiredfunctionality to fully complete the emergency call in the currentenvironment, then the AP will act as a proxy for the STA (step 914). Forexample, if the STA does not have SIP protocol support, then the AP canact as a SIP proxy for the STA. As another example, if the STA has SIPsupport but the network only supports H.323, then the AP can interworkthe SIP messages from the STA to H.323 messages to the rest of thenetwork. In the extreme case that the STA does not even have a vocoder,the AP can download a thin vocoder client to the STA and interwork tomore standard vocoders elsewhere in the network.

Another method is that the AP spoofs (i.e., reads the contents and/ortype information even if it is officially not supposed to) on thecontents of the IP packets that are used for signaling or normal trafficby the STA and its correspondent in the network. For example, SIPsignaling protocol messages over IP are typically used today for callhandling. Such SIP signaling contains useful information, such ascapability information and destination addresses, for the AP to fulfillits role as proxy. In addition to the previously described methods, ifthe AP extracts such information from spoofing on the STA-remotedestination higher layer (i.e., above L2 MAC) message contents, it canfulfill its role more efficiently. A person skilled in the art wouldrecognize that SIP is one example of a management protocol for IP-basedcalls, and that other equivalent protocols exist and are widely used inthe industry. Therefore, this method is not limited to SIP alone.

B. Linking an AP to an emergency call center

Once an AP learns of a STA making an emergency call, the AP needs toestablish a link to an emergency call center in order to properly routethe call from the STA. There are several possible transfer mechanisms toget the emergency call from the AP to the call center. For example, theAP can communicate with a gateway, linking it to the call center.

The emergency network node concept can be extended to include anemergency response operations center with man-in-the-loop capability.The emergency network node would be an extended service set (ESS) ornetwork tailored to the infrastructure application. For example, on auniversity campus, the designated emergency network node would be thecampus police department. As another example, in a manufacturing plant,the emergency network node would be the security office. The emergencynetwork node would include an operator who would receive the VoIP call,log call information, screen calls, and then place an emergency call ona public switched telephone network (PSTN) to alert the appropriateauthorities.

The emergency network node concept can be further extended to include anautomated node with a direct line to a PSTN. The automated node wouldact as voice circuit bridge to dial and connect the wireless caller tothe PSTN emergency center.

The method for connection to the emergency network node could beextended to include the ability to route and handle a call withoutauthentication, authorization, or security features. This would permit adirect unencrypted connection or a tunneled connection between thewireless caller and the emergency network node.

The function of the emergency network node could be extended to includecall handing, call handoff, and roaming coordination. This functionalitywould preauthorize resources in neighbor APs (APs adjacent to the APserving the wireless call), so that the caller may roam without losingthe wireless connection and without the need to reestablish a newemergency call when moving across AP boundaries, thus eliminatingduplicate calls on same emergency.

The concepts of the present invention can be extended beyond thespecific examples illustrated above. For example, the present inventioncan be extended to mesh networks and ad-hoc networks. As an alternative,instead of a human user, the present invention can be extended tomachine-to-machine usage scenarios for emergency handling with WLANs.One possibility would be using 802.11 in home security systems, i.e., aWLAN is used in place of hard wired telephone lines (that can be cut).In this example, instead of a human user generating a WLAN emergencycall, the home security system auto-generates an emergency call to asecurity call center when someone breaks in. Alternatively, the homesecurity system could start sending emergency SOS frames, as describedabove.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone (without the other features andelements of the preferred embodiments) or in various combinations withor without other features and elements of the present invention.

1. A method for use in a wireless transmit/receive unit (WTRU), themethod comprising: communicating with a cellular network; communicatingwith an Institute of Electrical and Electronics Engineers (IEEE) 802wireless local area network (WLAN); receiving an indication via the IEEE802 WLAN that the IEEE 802 WLAN has priority over the cellular networkwith regard to an emergency call, wherein the indication is a bit flag,an emergency message type information element (IE), an emergency messagefield, or an emergency call code; determining that the IEEE 802 WLAN isnot available to process the emergency call; and initiating theemergency call using the cellular network.
 2. The method of claim 1,wherein the IEEE 802 WLAN utilizes an 802.11* WLAN technology.
 3. Themethod of claim 2 wherein the cellular network utilizes a UniversalMobile Telecommunications System (UMTS) technology.
 4. The method ofclaim 1, wherein the indication is received in a medium access control(MAC) frame.
 5. The method of claim 1, wherein the indication isreceived in a control frame, a management frame, or a data frame.
 6. Awireless transmit/receive unit (WTRU), comprising: a processorconfigured to communicate with a cellular network and an Institute ofElectrical and Electronics Engineers (IEEE) 802 wireless local areanetwork (WLAN); and a receiver configured to receive an indication viathe IEEE 802 WLAN that the IEEE 802 WLAN has priority over the cellularnetwork with regard to an emergency call, and wherein the receiver isconfigured to receive the indication as a bit flag, as an emergencymessage type information element (IE), as an emergency message field, oras an emergency call code; wherein the processor is configured todetermine that the IEEE 802 WLAN is not available to process theemergency call and initiate the emergency call using the cellularnetwork.
 7. The WTRU of claim 6, wherein the processor is configured tocommunicate with an IEEE 802 WLAN that utilizes an 802.11 WLANtechnology.
 8. The WTRU of claim 7 wherein the processor is configuredto communicate with a cellular network that utilizes a Universal MobileTelecommunications System (UMTS) technology.
 9. The WTRU of claim 6,wherein the receiver is configured to receive the indication in a mediumaccess control (MAC) frame.
 10. The WTRU of claim 6, wherein thereceiver is configured to receive the indication in a control frame, amanagement frame, or a data frame.
 11. A method for use in a wirelesstransmit/receive unit (WTRU), the method comprising: communicating witha cellular network; communicating with an Institute of Electrical andElectronics Engineers (IEEE) 802 wireless local area network (WLAN);receiving an indication via the IEEE 802 WLAN that the cellular networkhas priority over the IEEE 802 WLAN with regard to an emergency call,wherein the indication is a bit flag, an emergency message typeinformation element (IE), an emergency message field, or an emergencycall code; determining that the cellular network is not available toprocess the emergency call; and initiating the emergency call using theIEEE 802 WLAN.
 12. The method of claim 11, wherein the IEEE 802 WLANutilizes an 802.11 WLAN technology.
 13. The method of claim 12 whereinthe cellular network utilizes a Universal Mobile TelecommunicationsSystem (UMTS) technology.
 14. The method of claim 11, wherein theindication is received in a medium access control (MAC) frame.
 15. Themethod of claim 11, wherein the indication is received in a controlframe, a management frame, or a data frame.
 16. A wirelesstransmit/receive unit (WTRU) comprising: a processor configured tocommunicate with a cellular network and an Institute of Electrical andElectronics Engineers (IEEE) 802 wireless local area network (WLAN); anda receiver configured to receive an indication via the IEEE 802 WLANthat the cellular network has priority over the IEEE 802 WLAN withregard to an emergency call, and wherein the receiver is configured toreceive the indication as a bit flag, as an emergency message typeinformation element (IE), as an emergency message field, or as anemergency call code; wherein the processor is configured to determinethat the cellular network is not available to process the emergency calland initiate the emergency call using the IEEE 802 WLAN.
 17. The WTRU ofclaim 16, wherein the processor is configured to communicate with anIEEE 802 WLAN that utilizes an 802.11 WLAN technology.
 18. The WTRU ofclaim 17 wherein the processor is configured to communicate with acellular network that utilizes a Universal Mobile TelecommunicationsSystem (UMTS) technology.
 19. The WTRU of claim 16, wherein the receiveris configured to receive the indication in a medium access control (MAC)frame.
 20. The WTRU of claim 16, wherein the receiver is configured toreceive the indication in a control frame, a management frame, or a dataframe.